Wood-preserving compositions are well known for preserving wood and other cellulose-based materials, such as paper, particleboard, textiles, rope, etc., against organisms responsible for the destruction of wood, including fungi and insects. Many conventional wood-preserving compositions contain copper-amine complexes. Copper-amine complexes have been used to solubilize copper in aqueous solutions. The copper in such copper-amine complexes is obtained from a variety of copper bearing materials, such as copper scrap, cuprous oxide, copper carbonate, copper hydroxide, a variety of cuprous and cupric salts, and copper bearing ores. The amine in such copper-amine complexes is normally obtained from an aqueous solution of ammonia and ammonium salts, such as ammonium carbonate, and ammonium sulfate, ethanolamines, and the like. For example, U.S. Pat. No. 4,622,248 describes forming copper-amine complexes by dissolving copper (II) oxide [CuO] (also known as cupric oxide) in ammonia in the presence of ammonium bicarbonate.
The disadvantage of using ammonia as a copper solubilizing agent lies in the strong odor of ammonia. Additionally, copper-ammonia preservatives can affect the appearance of the treated wood giving surface residues and undesirable color. In recent years, many amine-containing compounds, such as alkanolamines and aliphatic polyamines, have been used to replace ammonia to formulate water-soluble copper solutions. These compounds were chosen because of their strong complexing ability with copper and because they are essentially odorless. U.S. Pat. No. 4,622,248 discloses a method of preparing copper-amine complexes by dissolving a mixture of copper (II) carbonate [CuCO3] and copper (II) hydroxide [Cu(OH)2] in ethanolamine and water. The complexing amine (i.e., the ligand) and copper (II) ion combine stoichiometrically and thus the weight ratio of reagents will be different for each complexing amine. However, copper-amine based preservatives have higher copper loss due to leaching as compared to traditional copper-based preservatives such as chromated copper arsenate (CCA).
In addition to metal biocides, existing wood preservatives can also contain organic biocides. However, many organic biocides currently in use are not water soluble. Therefore, solubilizing agents, surfactants and wetting agents are often added to either solubilize or form emulsions of the organic biocide to formulate a product that is suitable for the treatment of wood or other cellulose substrates.
However, the solubilizing agents, surfactants, and wetting agents are costly and the use of these products may result in enhanced leaching of the biocides when the treated material comes into contact with moisture. Such enhanced leaching is considered to be the result of the solubilizing agents, surfactants and wetting agents which remain in the wood after treatment. Because these compounds continue to cause leaching of the metal and/or biocide from the treated wood, field performance problems or environmental issues can result.
Despite many efforts to address these deficiencies in existing wood preservatives, there has been an unmet need to produce aqueous metal-based preservatives that are suitable for treating wood and other cellulose-based materials while minimizing the undesirable leaching of metal ions and/or biocide from treated materials when exposed to water. This need is met by the invention disclosed herein.